524 COMPARATIVE. HISTORICAL. 



stances, retention of urine takes place (a) because the division of the spinal cord 

 gives rise to increased reflex activity on the part of the urethral sphincter, and (b) 

 because inhibition of this reflex cannot take place. If, with increasing distention 

 of the walls of the bladder, the urethral orifice is finally dilated mechanically, 

 dribbling of urine takes place. Nevertheless, the urine escapes only drop by 

 drop, as it overcomes the maximum tension at which the urethra still closes. 

 Therefore, the bladder becomes more and more distended, as the tone of the 

 continuously stretched walls lessens progressively, and the bladder may be 

 distended to an enormous size. In consequence of the entrance of bacteria into 

 the bladder, ammoniacal decomposition of the long-retained urine may readily 

 take place; and, as a result, catarrhal and inflammatory conditions of the bladder 

 may be excited. (4) From interference with the voluntary control of the 

 inhibition of the reflex of the urethral sphincter, as well as from increased reflex 

 excitability of the urethral center. 



Incontinence of urine stillicidium urinas occurs as a result (i) of paralysis 

 of the urethral sphincter; (2) of anesthesia of the urethra, in consequence of 

 which the reflex of the sphincter must be lost; (3) incontinence of urine is, sec- 

 ondarily, always a result of division of the spinal cord or of abnormal degeneration. 

 Strangury is observed as an excessive reflex of the walls of the bladder and the 

 sphincter muscle, in consequence of irritation of the bladder and the urethra, as 

 observed in association with inflammation, irritation, and neuralgia. So-called 

 nocturnal enuresis, nocturnal involuntary discharge of urine, may be a result of 

 increased reflex activity of the walls of the bladder, or of enfeeblement of the 

 reflex of the sphincter muscle. Nothing of a definite nature is known as to the 

 influence of deranged action of the will,. principally in connection with unilateral 

 injury, apoplexy, and the like. In patients suffering from disease of the spinal 

 cord, there is impairment of the sensation of a distended bladder, as well as of 

 the contractile power of the walls of the bladder. In neurasthenic patients, the 

 latter is diminished, while the sensation of distention is increased. In patients 

 with prostatic disease, there is, at first, likewise increased sensitivity with a dis- 

 tended bladder. 



COMPARATIVE. HISTORICAL. 



In vertebrates, with exception of the bony fishes, there is often a union of the 

 urinary and the generative organs. The primitive kidney (Wolffian body), which 

 serves during the first period of embryonic life as an excretory organ, assumes 

 this function throughout life in fish and amphibia. The myxenoids (cyclostomata) 

 possess the simplest kidneys : On either side there is a long ureter, upon which are 

 situated capsules with short pedicles containing glomeruli, and arranged in rows. 

 Both ureters empty into the genital pore. In the remaining fishes, the kidneys 

 often extend longitudinally, lying as more compact masses on either side of the 

 vertebral column. The two ureters unite to form the urethra, which always 

 opens behind the anus, either united with the genital orifice or behind this. In 

 the sturgeon and the shark the anus and the urethral orifice together form a 

 cloaca. Bladder-like formations, which, however, do not resemble the urinary 

 bladder of mammalia morphologically, occur in fish, either at each ureter (ray, 

 shark) or at the junction of the two. 



In amphibia, the efferent vessels of the testicles unite with the urinary tubules. 

 The testicular-renal duct unites, in the frog, with that of the other side; and both, 

 united, open into the cloaca, while the capacious urinary bladder opens through 

 the anterior wall of the cloaca. 



From the reptiles upward, the kidney in all vertebrates is no longer the per- 

 sisting Wolffian body, but a newly formed organ. In reptiles, it is generally 

 flattened longitudinally. The ureters open separately into the cloaca. Saurians 

 and tortoises possess a bladder opening into the anterior wall of the cloaca. In 

 birds, the ureters remain separate and open into the urogenital sinus emptying 

 into the cloaca internally to the excretory ducts of the generative glands. The 

 bladder is constantly wanting. In mammalia, the kidneys often consist of many 

 small lobules, reniculi, as, for instance, in the seal, the dolphin, the ox. 



Among invertebrate animals, molluscs possess excretory organs in the form 

 of canals provided with an external opening and an internal opening, communi- 

 cating with the cavity of the body, and occasionally functionating also as oviducts. 

 In mussels, this canal is expanded into a spongy organ (organ of Bojanus) , situated 

 at the base of the gills, often possessing a central cavity of considerable size, and 



